The present invention relates to a process for the production of a thinned electric part. Specifically, the process is characterized in that a resin composition containing a swelling inorganic compound (WC) is used for part or the whole of an adhesion layer and a separation is promoted due to a decrease or loss in the adhesive strength of the adhesion layer by making the swelling inorganic compound (WC) absorb a liquid after the completion of a treatment step of a back surface. In particular, the process enables a separation in cases where the separation is extremely difficult, such as a case in which an adhesive strength is strengthened by a treatment step such as a treatment step essentially requiring a high temperature step.
In recent years, electronic devices have been desired to be decreased in thickness or in weight. As is typified by a portable telephone or an IC card, electric devices are decreasing in thickness. From the viewpoint of a speed-up or a decrease in electric power consumption, it is required to decrease the thickness of a semiconductor.
When electric circuits are formed on only one surface of a semiconductor wafer, a ceramic substrate and etc. (to be generically referred to as xe2x80x9csubstratexe2x80x9d hereinafter) which have been already thinned, warps or distortions occur due to a thermal expansion coefficient difference of approximately 5xcx9c15xc3x9710xe2x88x926Kxe2x88x921 between a material for the formation of circuits, particularly a metal such as aluminum, copper or gold, and the silicon wafer or the ceramic substrate. Due to the occurrence of warps or distortions, it becomes impossible to form circuits on its back surface and furthermore it becomes also impossible to carry out even all steps of the front surface in some cases. For this reason, it is substantially impossible to use a substrate which has been already thinned.
Thus, conventionally, when electric circuits are formed on only one surface, there is adopted a method in which an electric-circuits-forming step essentially requiring a high temperature is performed mainly on one surface (front surface) of a substrate having a thickness, generally at least 200 xcexcm, sufficient for retaining the shape thereof, then the front surface is bonded to a holding substrate to protect the front surface, and the opposite surface (back surface) is polished to thin the substrate.
Conventionally, as a thinning method, there is proposed a fixation method with a wax or a tape.
As a fixitation method using a wax, there is proposed a method in which a wax is applied on a dummy wafer (holding substrate) under heat, a wafer is bonded to the dummy wafer, the wafer is ground and further polished and then the wafer is separated from the dummy wafer by melting the wax under heat and slipping the wafer sideways or by cooling the wax and breaking the wax which has become fragile by means of an impact breakdown. However, the wax fixation has problems about thickness accuracy, parallelism and flatness.
As a tape fixation method, there is a method in which a back-grinding tape is affixed to a front surface of a substrate and an opposite surface is polished to thin the substrate.
When it is required to form a metal thin layer on the back surface of a thinned wafer or a thinned substrate, generally, there is required a high-temperature treatment step at a temperature of from 250 to 450xc2x0 C. for from 30 minutes to 1 hour, which high-temperature treatment includes, for example, a pretreatment with fluoric acid, nitric acid or the like, a metal deposition such as aluminum or gold, and a calcination treatment thereof.
However, it is impossible to carry out these steps under the state where a substrate is bonded to a holding substrate with a wax or a back-grinding tape. In the method using a wax or a tape for thinning, after a substrate is thinned, it is separated from a holding substrate and then subjected to a high-temperature treatment step. The thinned substrate is very fragile. And, since semiconductor circuits different in thermal expansion coefficient from the substrate exist on one surface of the thinned substrate, a defective fraction considerably increases because of distortion or breakage. Further, when the thickness is thin or approximately 50 xcexcm, it is difficult to subject the thinned substrate to a high-temperature treatment step.
If electric circuits can be efficiently formed on a thinned substrate having a large work size, electric parts having a decreased thickness, a high speed and a decreased electric power consumption can be practically produced.
Thus, the present inventors have proposed a method in which a substrate is bonded to a holding substrate, the substrate is thinned, the thinned substrate bonded to the holding substrate is subjected to a high temperature treatment step or other steps as it is and, after the completion of these steps, the substrate is separated from the holding substrate by using water or the like (JP-A-2001-77304, Japanese Patent Application Nos. 2001-30746, 2000-401077, 2000-401078, etc.).
However, in the above method, when a treatment step at more than 400xc2x0 C. is present, the separation is substantially impossible.
Further, even when no high temperature treatment step is present, depending on a surface-treatment method of a substrate, it is very difficult in some cases to find a resin composition for bonding which has an adhesion reliability sufficient for enduring a processing step of a back surface and allows an easy separation after the completion of the step.
It is an object of the present invention to provide a resin composition for bonding which can be easily decreased in adhesive strength by a simple means even when an adhesion is strengthened by a high-temperature treatment step or even when it is difficult to find an easily-separable resin composition for bonding, and provide its use.
According to the present invention, there is provided a process for the production of an electric part, comprising performing a circuit-parts-forming step including the introduction of impurities on one surface (surface A) of a semiconductor substrate, then bonding the surface A to a holding substrate, performing a back surface treatment step essentially including a polishing of an exposed surface (surface B) of the semiconductor substrate to a thickness of 100 xcexcm or less to obtain an electric-part-formed thinned substrate and separating the thinned substrate from the holding substrate, wherein a resin composition containing a swelling inorganic compound (WC) is used for an adhesion layer and in the separating step the thinned substrate is separated from the holding substrate after decreasing the adhesive strength of the thinned substrate and the holding substrate by swelling the swelling inorganic compound (WC).
Further, in the process provided according to the present invention, preferably, the swelling inorganic compound (WC) is a fine powder having an average particle diameter of from 0.05 to 3 xcexcm.
Further, in the process provided according to the present invention, preferably, the swelling inorganic compound (WC) contains substantially no particles having a particle diameter of 10 xcexcm or more.
Further, in the process provided according to the present invention, preferably, the swelling inorganic compound (WC) is a swelling clay mineral, a swelling phyllosilicate or a swelling carbon.
Further, in the process provided according to the present invention, preferably, the content of the swelling inorganic compound (WC) in the resin composition is 1 to 30% by weight.
The constitution of the present invention will be explained hereinafter.
The present invention is characterized in that a resin composition containing a swelling inorganic compound (WC) is used in an adhesive layer.
The swelling inorganic compound (WC) is an inorganic compound which gets swollen by absorbing water, an organic solvent, steams of these, etc. Generally, the above inorganic compound has a layered crystal structure and has a hydrophilic or lipophilic element or a hydrophilic or lipophilic group in the interlayer, and the interlayer adsorbs water or an organic solvent molecule to broaden an interlayer distance or cause a delamination in some cases. The swelling inorganic compound (WC) includes a water-swelling clay mineral, a swelling phyllosilicate or a swelling carbon.
The water-swelling clay mineral includes sepiolite, palygorskite, vermiculite, bentonite, sericite clay, etc.
The swelling phyllosilicate includes a natural product and a synthetic product. The natural swelling phyllosilicate includes natural bentonite, natural hectorite, natural saponite, natural stevensite, natural beidellite, natural montmorillonite, natural nontronite, etc.
The synthetic swelling phyllosilicate includes a synthetic smectite, a synthetic hectorite, a synthetic swelling mica, etc.
The synthetic smectite includes synthetic products of hectorite, saponite, iron saponite, stevensite, beidellite, montmorillonite, nontronite, etc.
The synthetic swelling mica includes a Li type taeniolite, a Na type taeniolite, a Na type hectorite, a Na type tetrasilicic mica, a Li type tetrasilicic mica, a synthetic swelling fluorinated mica, a Na type fluorinated tetrasilicic mica, etc.
The swelling carbon includes swelling graphite, etc.
Commercially available products of the swelling inorganic compound (WC) include Somacigh (product No.; ME-100, supplied by Co-op chemical Co., Ltd., synthetic swelling mica), Rucentite (product Nos.; SWN, SWF, SHS, supplied by Co-op chemical Co., Ltd., synthetic smectite), Dymonite (supplied by Topy Industries, Ltd., synthetic swelling mica), Sgmeton SA-1(supplied by Kunimine Industries Co., Ltd., saponite allied substance), Kunipia F (supplied by Kunimine Industries Co., Ltd., natural montmorillonite),Bengel (supplied by HojunYoko K.K., natural montmorillonite), Beegahm (supplied by Vanderbilt (USA), natural hectorite), Laponite XLG (supplied by Laporte Industries Ltd (UK), natural hectorite allied substance), Laponite RD (supplied by Laporte Industries Ltd(UK), synthetic hectorite allied substance), and Thermobis (supplied by Henkel (Germany), synthetic hectorite allied substance).
A synthetic smectite imparted with an organic solvent-swelling property, i.e., lipophilic property includes Rucentite (SAW, SAF, STN, SPN; type of being swollen with a toluene or xylene solvent, supplied by Co-op chemical Co., Ltd., organic synthetic smectite) and Rucentite (SEN, STN, SPN, DMF; type of being swollen with a pyrolidone solvent, supplied by Co-op chemical Co., Ltd.).
While the average particle diameter of the swelling inorganic compound (WC) is generally 0.01 to 10 xcexcm, the average particle diameter is preferably 0.05 to 3 xcexcm and it is more preferred that the swelling inorganic compound (WC) has no particles having a diameter of 10 xcexcm or more. A bonding surface is a semiconductor-circuit-formed surface and the adhesion layer must has a uniform thickness and be homogeneous. Therefore, the existence of particles having a large particle diameter is undesirable, since it inhibits a homogenous adhesion. Further, the swelling inorganic compound (WC) preferably has high compatibility with a resin in view of forming a more homogenous stable layer in the preparation of a film for adhesion or the formation of an adhesion layer by a spin coating or the like. Thus, it is preferred to adopt a method in which the swelling inorganic compound (WC) is surface-treated with a surface-treating agent or a method in which a surface-treating agent is added into a resin to be incorporated in advance or at the time of preparing a composition, as required. As a surface-treating agent used therefor, there is used a silane surface-treating agent, a titanium surface-treating agent or an aluminum surface-treating agent.
The resin composition of the present invention containing the above swelling inorganic compound (WC) is used as a beforehand-produced film or a multilayered film having a layer of the above resin composition on at least one surface thereof. Otherwise, a resin solution thereof is applied on a holding substrate by a spin coating method or other methods to form an adhesion layer on the holding substrate.
The resin used for the resin composition of the present invention must be mixable with the swelling inorganic compound (WC). Examples thereof include a liquid resin, a resin able to used as a resin solution, or a thermoplastic resin.
The thermoplastic resin includes a thermoplastic polyimide, polyetherimide, polyamide imide, polyether ketone, polyether ether ketone, polybenzoimidazole, polyamide, polyvinyl alcohol, polystyrene, triacetylcellulose, poly-4-methylpentene, an ethylene-vinylalcohol copolymer, polymethyl methacrylate, a fluorine tetrafluoroethylene-fluoroalkylvinylether copolymer (PFA), polyvinylidene fluoride (PVDF), a tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE) and a chlorotrifluoroethylene-ethylene copolymer (E/CTFE).
Further, a resin solution used for forming a heat-resistant adhesion layer includes solutions of polyimide acid of a polyimide precursor in dimethylformamide (DMF), dimethylacetamide (DMAC) or N-methyl-2-pyrolidone. In addition to these, various thermoplastic resins can be used as a solvent solution thereof. Example thereof includes a solution of a thermoplastic polyamide resin (crystalline nylon) in formic acid, mineral acid, phenols or fluoroalcohol; a solution of 6/6-6 nylon or 6/6-10 nylon in heated methanol; a solution of polyvinyl alcohol or an ethylene-vinyl alcohol copolymer in alcohols; a solution of polystyrene or methyl methacrylate in a ketone or an aromatic hydrocarbon; and a solution of a polycarbonate resin or a polyphenyleneether resin in a hologenated hydrocarbon solvent.
The adhesion layer of the present invention is formed from the above components.
The adhesion layer is used as a beforehand-prepared film, a coating film or an adhesion auxiliary layer formed on a film.
First, examples of the method using as a coating film includes the following methods. In a first method, a swelling inorganic fine powder such as a synthetic smectite fine powder is incorporated into a resin solution such as a polyimide resin solution. The mixture is defoamed or mixed under a reduced pressure to obtain a coating composition having physical properties, particularly a viscosity, suitable for a means to be adopted. Then, the coating composition is applied on a holding substrate by a spin coating, a bar coating, a roll coating or a silk screen printing, dried and polymerized by heating. In a second method, coating layers same or different in kind are formed both on a substrate and on a holding substrate respectively and the coating layers are integrated at a bonding time to form an adhesive layer. In a third method, a layer of the above coating composition is formed on either a substrate or a holding substrate which is a predetermined separation side and a commercially available film is stacked on the above layer.
The method using as a beforehand-prepared film is typified by a method using a solventless mixture in which a swelling inorganic fine powder such as a synthetic smectite fine powder is mixed with, for example, a thermoplastic polyamide resin with a kneading machine and the kneaded mixture is extruded and then oriented as required to form a film. Further, there may be adopted a method in which a coating film is formed on a substrate to be separated by the same method as the above method of directly forming an adhesion layer and the coating film is separated and then used as an adhesion film.
Further, the above method includes a method in which film(s) of the above-mentioned coating composition is formed on one surface or both surfaces of a commercially available film to form a laminate film.
Further, as another method, there can be devised a method in which a holding substrate is held in a metallic mold and an adhesive layer is formed on its one surface by a press molding, an injection molding or the like.
Next, while the holding substrate of the present invention is selected depending on the condition of a back surface treatment step as required, the holding substrate of the present invention is needed to have high heat resistance and high chemical resistance. Further, it is needed for decreasing a warp after the bonding that the holding substrate has a coefficient of thermal expansion near to that of a substrate.
Generally, examples of the holding substrate includes inorganic compound-based materials such as aluminum nitride, silicon carbide, silicon nitride, sapphire, alumina, zirconia, wollastonite, amorphous carbon, glassy carbon and a C/C composite with silicon carbide. A silicon wafer can be also used.
Further, there are preferably used those which obtained by impregnating an inorganic continuously porous sintered body having preferably 2 to 35 vol % of continuous pores having an average pore diameter of 0.1 to 10 xcexcm with a heat resistant resin and curing the impregnated resin. The inorganic continuously porous sintered body includes aluminum nitride-boron nitride(AlN-h-BN), silicon carbide(SiC), aluminum nitride-silicon carbide-boron nitride (AlNxe2x80x94SiC-h-BN), alumina-boron nitride (Al2O3-h-BN) and silicon nitride-boron nitride (Si3N4-h-BN), zirconium oxide-alumina-boron nitride (ZrO3xe2x80x94Al2O3-h-BN), alumina-titanium oxide-boron nitride (Al2O3xe2x80x94TiO-h-BN) and amorphous carbon. In particular, inorganic continuously porous sintered bodies disclosed in JP-A-2000-344587 are preferably used.
For improving the adhesion of a bonding surface, the holding substrate preferably has a surface roughness Ra of from 0.1 to 5 xcexcm. When the adhesion of the bonding surface to an adhesion layer becomes worse, a separation occurs between the holding substrate and the adhesion layer at a separation time instead of a separation between the substrate and the adhesion layer. In this case, if no contrivance is given to a holding means of the substrate after the separation, undesirably, a warp or a breakage in some cases occurs. When the surface roughness Ra is larger than 5 xcexcm, the adhesion layer can not absorb the roughness to cause a wrinkle of the adhesion layer or a breakage of the substrate in some cases. Further, the surface of a substrate to be used should avoid having a surface roughness of more than 5 xcexcm. When such a roughness is essentially required, it is preferred to use a substrate of which the surface is smoothed by forming a protection layer for covering the roughness.
Further, a surface treatment is carried out for improving adhesive property. As a method therefor, the indispensable preliminary treatment for a resin impregnation, described in the above-mentioned JP-A-2000-344587, is the most preferable. In the above treatment, one kind or at least two kinds of organic metal compound(s) (M) is impregnated so as to arrive at the surfaces of pores of the holding substrate, air-dried, preliminarily reacted, dried under heat and further pyrolyzed at a maximum temperature of 850xc2x0 C. or less.
As a method for separating the thinned substrate of the present invention from the holding substrate, there can be adopted methods disclosed in Japanese Patent Application Nos. 2000-194077, 2001-30746, 2000-401077, 2000-401078, etc. Further, when a lipophilic swelling inorganic compound (WC) is used for the bonding, there can be adopted a method in which an appropriate organic solvent is selected and used for promoting the separation.
Furthermore, there can be adopted, as required, a method in which after cutting to respective chip sizes, a separation is promoted to separate the thinned substrate from the holding substrate and a method in which the adhesion layer-attached substrate is separated from the holding substrate with the thinned substrate being held by adsorption and then the adhesion layer is separated by further carrying out a separation-promoting treatment.
The state of a semiconductor circuit formed on a bonding surface (front surface), for example an aluminum metal corrosion by an aluminum metal exposure, limits the selection of a separation-promoting method in some cases. In such cases, a separation promotion using an organic solvent is selected.